Synchronization of neuronal activity within and across brain regions is a fundamental property of cortical and subcortical networks needed for normal brain functions. Synchronization of electroencephalogram (EEG) in the frequency range of 1-4 Hz, referred to as slow wave activity (SWA), is observed during slow wave sleep and is thought to be essential for the recuperative function of sleep. Recent work in our laboratory found that changes in SWA parallel the changes in the activity of neuronal nitric oxide synthase (nNOS)-immunoreactive cells in the cortex in three mammalian species. These results suggest that nNOS neurons in the cortex are part of the brain circuit that is involved in the generation of SWA. Since SWA is an established marker of the homeostatic sleep drive, the nNOS neuronal circuit is expected to be activated by homeostatic mechanisms. The proposed studies will test the following hypotheses: (1) changes in the activity of nNOS cells in the cortex correlate with SWA, (2) changes in the activity of nNOS cells in the cortex are independent of circadian input from the suprachiasmatic nucleus, (3) anatomical properties of nNOS cells are consistent with the role of these neurons in EEG synchronization, (4) nitric oxide production by nNOS is involved in SWA generation, and (5) selective ablation of nNOS cells leads to disturbances in SWA production and sleep homeostasis. This research will be a first step in characterizing newly discovered sleep-active neurons in the cortex. It will provide important information about regulation of brain activity by nNOS neurons and may advance our understanding not only of the pathophysiology of sleep disorders, but also of neurological and psychiatric diseases that involve the cerebral cortex.